Streamer mechanism for negative corona current pulses

Abstract

Current wave forms of initial stages of breakdown and corona formation in a short negative point-to-plane gap have been measured with a nanosecond time resolution in air, O2, and N2 at pressures 13.33–100 kPa, and at various overvoltages. The experiments revealed the existence of a stepped form of negative corona Trichel pulses in O2 at atmospheric pressure. To test existing models for the negative corona pulse formation, effects of changing cathode secondary electron emission were studied using a brass cathode coated by CuI and graphite. It is concluded that a negative corona (Trichel) pulse is associated with the ignition of a cathode-directed streamer in the immediate vicinity of the cathode and the subsequent formation of a glow-discharge-type cathode region at the streamer arrival to the cathode. The implications of these results to negative corona applications are discussed.

Negative Corona Current Pulses in SF6– Air Mixtures

“…The stepped pulse waveforms measured for SF 6 admixtures less than approximately 10% (see Figs. 3 -4) agree well with the characteristics of the stepped negative corona pulses observed in oxygen [9,17], nitrogen [8,9], CO 2 [12], and CO [11] at reduced gas pressures using large cathode point radii (more than 0.2 mm).…”

“…At atmospheric pressure, reliable results on reproducible stepped negative corona pulses have been hitherto obtained only for N 2 /SF 6 mixtures [6,16] and oxygen [9]. The results in Fig.…”

“…The present study emerges from our previous work on the negative corona mechanism in N 2 -SF 6 mixtures [7], N 2 -O 2 mixtures [8], O 2 [8,9,10 ], CO [11], and CO 2 [12], which in contrast to theories by Loeb [13] and Morrow [14,15] indicate that the ionisation mechanism controlling the negative pulse formation is a feed-forward-to-gas streamer mechanism, where secondary electrons supporting the development of the cathode-directed streamer can be produced in the gas by, for example, gas photo-ionization. The streamer-based model for negative corona pulses could well have practical significance also for the design of high-voltage gas-insulated apparatus [9], however, it is not certain to what extent this model applies in the case of SF 6 -air mixtures, and other SF 6 -based gas insulation mixtures. The aim of this work is to check for the validity of the streamer-based model of negative corona pulses also for SF 6 -air mixtures.…”

“…This issue is intimately connected with clarification of the exact roles played by electron photoemission and electron attachment. To clarify the role of photoemission, copper iodide and graphite, which have exceptionally high and exceptionally low photoelectric yields, respectively, were used as alternative cathode surface materials to copper [9]. The effects of electron attachment on the first negative corona pulse waveforms were assessed by changing the relative concentration of SF 6 .…”

Electric and Spectroscopic Studies of Pulsed Corona Discharges in Nitrogen at Atmospheric Pressure

“…Several studies of corona discharge ignited in nitrogen by the pulsed voltage at atmospheric pressure were carried out to provide more detailed on the discharge behavior and breakdown mechanisms [7] [8] [9] [10] [11]. Furthermore, N 2 is also chosen because it's the dominant gas of ambient air in the atmosphere and is broadly used in many industrial and technical applications as for instance plasma nitriding and surface treatments.…”